The Red Sox acquired their 2013 closer by trading for Hanrahan last week –- a decision likely based on the 36 saves and 2.72 ERA he posted last year. But does he really have the stuff of an elite ninth-inning guy?

Let's look closer at his stats.

Hanrahan’s sub-3.00 ERA and batting average allowed of .187 were supported by an unusually high strand rate and low BABIP, two factors that will make it difficult for Hanrahan to replicate his 2012 season in 2013.

Largest Difference Between FIP and ERA
Relievers Last Season (min. 50 IP)

His percentage of baserunners stranded (89.7 percent) and BABIP (.230) both ranked in the top five among NL relievers with at least 50 innings last season and were far removed from his career averages of 75 percent and .306.

Though Hanrahan had an above-average strikeout rate in 2012, his walk rate jumped from six percent in 2011 to 14 percent in 2012 (fifth-highest in MLB) and his groundball rate fell by nearly 15 percentage points over the last two seasons.

This combination of statistics partly contributed to a 4.45 FIP (an ERA estimate based on strikeouts, walks, and home runs allowed), which ranked 118th out of 134 relievers with at least 50 IP

The Brewers continued their bullpen revamp by signing well-traveled lefty Mike Gonzalez earlier this week. Milwaukee spent almost all of last season with one lefty in its bullpen (Manny Parra), but will now likely have two with the signings of Gonzalez and swingman Tom Gorzelanny.

They join right-hander Burke Badenhop as newcomers brought in to shore up one of Milwaukee’s biggest weaknesses and give the Brewers multiple specializations.

Brewers Bullpen Ranks - 2012

Left-handed hitters had a .763 OPS against Brewers relievers last season. The only teams whose relievers fared worse against lefty hitters were the Miami Marlins and Chicago Cubs.

Gonzalez has held opposing lefties to a .200 batting average and .555 OPS over the last two seasons, 34 points and 96 points better than the major-league averages in those stats respectively. His forte is a slider that nets about four lefties out for every one he allows to reach base.

Gorzelanny has comparable numbers in that stretch (a .203 opponents’ batting average and .606 opponents’ OPS). Reds slugger Joey Votto figures to face Gorzelanny in big spots a few times this season. He’s 3-for-20 against the new Brewers lefty.

When Badenhop is going well, he excels against hitters from the right side. They were 3-for-their-last-31 against him in 2012.

He’s an interesting option against lefties too, particularly when a ground ball is needed. Last season, lefties hit .300 against him (up from .250 over the previous three seasons combined), but were only 1-for-30 when hitting a ground ball.

The Brewers infield defense, another liability at times last season, will have to be on its toes for Badenhop. His 57 percent ground-ball rate the last two seasons is considerably above the major-league average (46 percent).